SUBTHRESHOLD HYPEROXIA POTENTIATES TNF-ALPHA-INDUCED ICAM-1 EXPRESSION ON CULTURED PULMONARY MICROVASCULAR ENDOTHELIAL-CELLS

The effects of combined exposure to subthreshold hyperoxia and the inf lammatory cytokine tumor necrosis factor alpha (TNF-alpha) on the expr ession of intercellular adhesion molecule-1 (ICAM-1) were examined in bovine lung microvascular endothelial cells (BLuEC). The expression of total ICAM-1 was not affected by 50% hyperoxic conditions alone, indi cating that this level is subthreshold for BLuEC. In the presence of 5 ng/mL TNF-alpha, which has minimal influence on BLuEC alone, the amou nt of total ICAM-1 expression under 50% hyperoxia was higher than that in normoxic conditions (approximately 30%) throughout the culture per iod. The amount of soluble ICAM-1 that has been released into the cult ure medium increased after joint exposure to hyperoxia and TNF-alpha. These results suggest that exposure to subthreshold hyperoxia, which d oes not by itself cause damage to the endothelial cells or induce ICAM -1 expression, potentiates the effects of low-level TNF-alpha exposure .